contours go with which outer contour) out of exportstep.cpp, since
I'll need that to do filled contour export for the 2d file formats.
Also add user interface to specify fill color.
[git-p4: depot-paths = "//depot/solvespace/": change = 2057]
and their holes into their own advanced faces. So a single surface
with multiple outer contours generates multiple advanced faces.
Also turn the default chord tol down to 1.5 pixels, seems more
likely to make the exact surface Booleans work.
[git-p4: depot-paths = "//depot/solvespace/": change = 1975]
feared. Though I don't have rational surfaces or curves going yet,
and I don't have the stuff to handle holes or multiple outer
contours in a single surface.
[git-p4: depot-paths = "//depot/solvespace/": change = 1974]
